The traditional apnea monitor measures the electrical resistance across the chest to sense breathing. These apnea monitors have both positive and negative false alarms. The reason that it does not give alarm when a baby stops breathing is that noise is too weak to detect (weaker than noise). The reason that alarm goes off when the baby is healthy is the noise is to strong (stronger than the breathing signal). Where the noise comes from? The resistance of the chest is influenced by the liquid flow inside the body and the air flow in the lung. The present invention measures the change of chest volume instead of measuring the resistance of the chest.
Before an apnea happens, usually a baby moves a lot. It is helpful to have a warning when the baby moves too often. The present invention detects the frequency of movement of a baby and will give a warning if there is too much movement. Measuring the change of chest volume can not detect obstructive apnea. Measuring the actual airflow coming in and going out of the patient's nose or mouth is an important method to detect apnea including obstructive apnea.
U.S. Pat. No. 6,849,049 suggests to use a mass airflow sensor AWM2100V manufactured by Honeywell Inc as a sensor capable of accurately measuring a very small flow. How ever, the description of AWM2100V published by Honeywell gives a warning: “DO NO USE these products as safety or emergency stop devices, or in any other application where failure of the product could result in personal injury.”
The present invention comprises a portion that can detect actual gas flow going in and out of nose and mouth. The critical part is the gas flow sensor and gas differential flow sensor. The present design of gas flow meter and gas differential flow sensor is made extremely sensitive and reliable.